[en] In dense silicon nitride the effect of grain elongation on crack propagation was studied using scanning electron microscopy. The crack front profile could be interpreted by both intergranular and transgranular crack deflection. This crack front deflection was characterized by means of a median deflection angle, which was computed from the surface trajectories of stable cracks. This method was applied to the evaluation of cracks in a set of hot-pressed silicon nitride materials, in which the grain elongation was varied in a controlled way of changing the additive concentration. It was found that the crack front deflection at the start of the critical crack propagation increased with grain elongation. At the same time, it was observed that room temperature fracture toughness increased with the median deflection angle. This indicates that crack front deflection contributes to the correlation between fracture toughness and grain elongation. (orig.)

[en] Self-reinforced silicon nitride ceramics rely the generation of elongated grains that act as reinforcing elements to gain increases in fracture toughness. However, the size and number of the reinforcing grains must be controlled, along with the matrix grain size, to optimize the fracture toughness and strength. Furthermore, the toughening processes of crack bridging are dependent upon retention of these reinforcing grains during crack extension by an interfacial debonding process. Both the debonding process and the resultant toughening effects are found to be influenced by the composition of the sintering aids which typical are incorporated into the amorphous intergranular films found in these ceramics. Specifically, it is shown that the interface between the intergranular glass and the reinforcing grains is strengthened in the presence of an epitaxial SiAlON layer. In addition, the interface strength increases with the Al and 0 content of the SiAlON layer. Micromechanics modeling indicates that stresses associated with thermal expansion mismatch are a secondary factor in interfacial debonding in these specific systems. On the other hand, first principles atomic cluster calculations reveal that the debonding behavior is consistent with the formation of strong Si-0 and Al-O bonds across the glass-crystalline interface

[en] A method has been developed for characterizing the texture of hot pressed Si₃N₄-materials which, based upon the evaluation of ceramographic sections, permits the distribution of the actual aspect ratio of the β-Si₃N₄-grains and the texture to be determined. Good agreement was obtained between the results obtained by this method with those obtained by X-ray diffraction measurement of the texture. (orig.)

[en] A high frequency ultrasonic system with computer controlled data acquisition and analysis has been described. The system has been used to detect surface flaws in the size range of 20-300 μm in hot pressed silicon nitride. The detection technique is based on Rayleigh waves which are generated as a result of the mode conversion of compressional waves incident from water onto the surface of the test material at near the Rayleigh angle. The scattering of the Rayleigh waves by surface cracks has been detected, analysed in the time and frequency domains, and correlated with the size of the cracks

[en] The propertis of hot-pressed ceramics are influenced by those of the employed powders, additives and body and by the process mode at the time of hot pressing. On the basis of a data-analysis concept for the compaction curve and all process parameters relevant to uniaxial hot pressing and a pertinent program system, various examples are used to demonstrate the effects of additive content, powder processing and temperature-dependent load-application point on the compaction behavior of silicon nitride during hot pressing. The compaction curves show significant differences in post-load-point isothermic and isobaric holding phase of the hot-pressing process, thereby indicating the modified effect of various sintering mechanisms. (orig.)

[en] Aluminium metal matrix composites (AMMCs) are the fastest growing metal matrix composites (MMCs) for the applications in several fields i.e.; automobile, aerospace and structural. The properties of these composites depend upon the reinforcement and their fabrication methods. This study focused on the accumulation of the ceramic reinforcement, silicon nitride (Si₃N₄) to the aluminium (Al) matrix in different weight proportions. Further, the significant methods for developing these materials and their effect on the various properties of the Al-Si₃N₄ composites have also been reviewed. The microstructural properties indicate the more uniform distribution of the reinforcing particles within the matrix for these composites developed by powder metallurgy method. From the literature, it has been also concluded that the addition of the ceramic reinforcement with appropriate weight percentages enhances the mechanical and tribological properties of the composites. (topical review)

[en] Thin silicon nitride films on silicon substrates, obtained from dichlorosilane and ammonia, are characterized by structure, composition, physical, optical, chemical and electrical properties. Properties are dependent, to a large extent, on the deposition conditions and are generally similar to those of the films deposited by the ammonolysis of silicon tetrachloride and the nitridation of silane with ammonia. Silicon nitride obtained from dichlorosilane has attractive properties to use for device passivation. (author)

[en] In this study, β-Si₃(C_x,N_1−x)₄ Silicon Carbonitride was prepared by Self-Propagation High-Temperature Synthesis (SHS). And the influence of carbon on structure stability, mechanical and tribological properties of β-Si₃(C_x,N_1−x)₄ were investigated. The results showed that the solubility of carbon in β-Si₃(C_x,N_1−x)₄ was about 10 wt%, beyond which cubic-SiC segregated out of β-Si₃(C_x,N_1−x)₄ to form β-Si₃N₄/cubic-SiC composite. Regarding influences of carbon concentration on mechanical properties, the hardness of β-Si₃(C_x,N_1−x)₄ decreased from 1400 Hv to 1200 Hv with the increase of carbon concentration. Whereas, the fracture toughness of β-Si₃(C_x,N_1−x)₄ increased from 6.5 MPa · m^0.5 to 7.6 MPa · m^0.5 with the increase of carbon concentration. The tribological property studies revealed the anti-wear performance of β-Si₃(C_x,N_1−x)₄ was enhanced by the increase of carbon concentration. The dominated wear mechanism could be attributed to the abrasive wear by fracture. (paper)

[en] Published in summary form only

[en] We numerically simulate the generation of an optical frequency comb (OFC) in a microring based on the traditional Si₃N₄ strip waveguide and a temperature compensated slot waveguide. The results show that OFCs are susceptible to temperature with strip waveguide while they can keep stable when temperature changes 10 K in either low- Q (10⁵) or high- Q (10⁶) microcavity with the well-designed slot waveguide, which has great superiority in practical applications where the temperature drift of the cavity due to the intense pump or surrounding change is unavoidable. (paper)